1. Field of the Invention
The present invention relates to a bill identification apparatus fop use in an automatic vending machine, exchange machine, game machine, etc.
2. Description of the Related Art
Bill identification apparatuses fop determining the type and authenticity of bills ape conventionally proposed and described in Japanese Patent KOKOKU Publication Nos. 63-26918, 64-5854, fop example. These apparatuses ape designed so that sampling data are obtained by detecting colors and shades on various parts of the bills of magnetic particulates contained in ink on the bills by means of sensors as the bills are transported, and the obtained data ape compared with reference patterns. In these conventional bill identification apparatuses, authentic bill signals for types of bills corresponding to the reference patterns ape outputted only when all the data sampled in individual positions are within their respective tolerances with respect to data fop the reference patterns. Thus, the reliability of the classification and authentication depends solely on deviations between the values of the sampling data and the reference pattern data fop the individual positions. In order to reject false bills securely by means of this conventional system, therefore, the tolerances as criteria must be made considerably small. If the tolerances ape too small, however, authentic bills may possibly be concluded to be false when the values of the detected data are uniformly shifted due to stains all over the circulating bills.
To cope with fluctuations of the detected data attributable to soiling or aging of the bills, shifts of the detected data values due to changes of the ambient temperature, etc., an improved bill identification apparatus is proposed and described in Japanese Patent KOKOKU Publication No. 58-9990. According to this apparatus, detected data are corrected by means of the average of the data sampled in individual positions, and the corrected data are compared with reference patterns. If an authentic bill is partially changed in properties by soiling, in this case, however, it will inevitably be rejected as a false bill. Proposed in Japanese Patent KOKAI Publication No. 2-148383, moreover, is a bill identification apparatus which is arranged so that the relationships between reference data for individual bill types and frequency distributions are previously stored, and operations for decision are performed on the basis of the fuzzy theory. Even though the detected data themselves are subject to fluctuations, this apparatus carries out no corrective operation to maintain conformity between the detected data and frequency distribution data as a control, so that it cannot cope with aging or soiling of the bills or sensors.
Accurate determination of the type and authenticity of the bills requires decision operation using a number of sensors and sampling data. According to the conventional bill identification apparatuses, however, all the sampling data detected during the transportation of the bills are retained collectively until data for the last sampling position is detected to be ready for the execution of a decision process. Accordingly, memory means, such as a RAM, requires a large memory capacity, and an arithmetic unit is loaded heavily.